MAX 7000 - Short circuit when entering in ISP mode

Altera_Forum · ‎07-21-2008

Hello,

I am trying to implement an In system programming feature using a EPM7512AETC144-10 but I am having problem when the CPLD enters into ISP mode. It seems to trigger a short circuit. However this problem doesn't happen when I use USB byte Blaster. Is there a difference internally between using the byte blaster and driving the pins with a microcontroller? I was able to find out that pins 100 and 101 (see attached circuit) are the causes of the problem. Theses pins are connected to two drivers IRS 2113S through 10 nf capacitors. Is there a difference between theses pins (100 and 101) and other I/O pins? Can anybody see something wrong with this circuit? By the way, what exactly happens when the CPLD enters into ISP mode?

Any help will be greatly appreciated

Regards,

Cyril

Altera_Forum · ‎07-21-2008

You didn't tell, if the short circuit is observed in MAX7000 logic supply or in connected driver supply or output transistors. ISP operation is basically three-stating the outputs (and activating weak pull-ups). The MAX7000 to IR2113 interface seems dubious to me, I wonder if defined input conditions are achieved either in normal operation and MAX7000 unconfigured state?

Altera_Forum · ‎07-22-2008

I just found out yesterday that the short circuit happens in the driver circuit and not in the MAX7000 logic supply. You are probably right, the interface probably put the driver in an unstable state. I have to look a little deeper on this.

Thanks